DIFFUSION SPECTRUM MRI OF STRUCTURAL CHANGES IN WHITE MATTER IN DEMENTIA

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 这个项目的总体目标一直是开发稳健的方法，使用扩散光谱成像来分析大脑连接。我们在采用一种方法方面取得了进展，这种方法能够以最小可能的偏见发现相关结构。我们设计的方法是对任何纤维路径分析满足它的所有其他路径的集合，即通过共享一个共同的体素。这代表了路径邻接的简单定义，相当于指定路径空间上的拓扑，因此是最基本的几何属性之一。路径邻接包括常见的端到端连通性作为特例，但也在3维中测量路径接近的其他方面，包括路径相切和路径交叉，因此它代表了对光纤路径的3D关系结构的高度公正的探测。我们报告了一种分析纤维连接的新方法的结果，该方法通过将这些方法应用于多种灵长类物种的扩散光谱成像(DSI)MRI。先前的纤维束造影术表明纤维交叉是零星的，而邻接显示交叉是普遍的和高度有组织的。我们发现近直角光纤交叉的网状或网格作为路径组织的基本单元。在每个位置，大脑白质被分解成相交的纤维路径的双轴系统，类似于织物的经线和纬线。我们称其为直线型结构。因此，不同深度的双轴结构是平行-外在平行的，因为平面与3D中的2D表面局部平行，并且还本质上平行，因为每个薄片内的两个纤维群体中的每一个都与另一个薄片中的对应纤维平行。在许多地方，还观察到了第三组垂直于其他两条路径的路径。似乎网状网络在整个大脑中都是连续的，而不仅仅是分散在不同的位置。这些结果揭示了我们所描述的直线性组织的连接模式的新的和简化的观点。它是所有脊椎动物脊髓和脑干的特征的纵向、双侧和背腹连接的简单模式的延伸。此外，已知的纤维路径都在这个正交线性方案中被识别，并且都依附于它，但现在被视为不同的结构，而更多地被视为特定方向路径的局部凝聚。这个新发现的组织代表了大脑的一个绝对的、自然的坐标系。这个自然的坐标系，就像它在中枢神经系统更尾部的实例一样，可能表达了大脑进化和发育的逻辑和方式，并将提供大脑结构和变异的自然框架描述。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The overall goal of this project has been to develop robust methods for analysis of brain connectivity using diffusion spectrum imaging. We have made progress in adopting an approach that enables discovery of correlated structures with the least possible bias. The approach we devised is to analyze for any fiber pathway the set of all other pathways that meet it, i.e by sharing a voxel in common. This represents a simple definition of path-adjacency, equivalent to specifying a topology on the space of paths, and so is among the most basic of geometric properties. Path-adjacency includes familiar end-to-end connectivity as a special case, but also measures other aspects of path proximity in 3-dimensions, including path tangency and path crossing, and so it represents a highly unbiased probe of the 3D relational structure of the fiber pathways. We report the results of a new way of analyzing the fiber connectivity revealed by applying these methods to diffusion spectrum imaging (DSI) MRI in multiple primate species. Whereas previous tractography has suggested that fiber crossing is sporadic, adjacency reveals crossing to be to be pervasive and highly organized. We have discovered a mesh or grid of near right-angled fiber crossings as a basic unit of path organization. At each location, cerebral white matter is resolved into biaxial systems of intersecting fiber pathways, resembling the warp and weft of fabric. We term this an ortholinear structure. Thus, bi-axial structure at different depths is parallel - extrinsically parallel, inasmuch as the planes are locally parallel as 2D surfaces in 3D, and also intrinsically parallel, as each of the two fiber populations within each sheet is parallel to its counterpart in the other sheet. In many locations, a third set of pathways perpendicular to the other two is also observed. It appears the mesh network is continuous throughout the entire brain and not simply in discrete locations. These results reveal a new and simplified view of the pattern of connections that we have described as an ortholinear organization. It is an extension of the simple pattern of longitudinal, bilateral and dorso-ventral connectivity that characterizes the spinal cord and brainstem of all vertebrates. Further, known fiber pathways are all recognized within this ortholinear scheme, and adhere to it, but now are seen less as distinct structures than as local condensations of pathways of a particular orientation. This newly revealed organization represents an absolute, natural coordinate system of the brain. This natural coordinate system, like its instantiations in the more caudal segments of the CNS, likely expresses the logic and means of brain evolution and development, and will provide a natural framework description of brain structure and variation.